1. Field of the Invention
The invention generally relates to a process of making a calcium fortified yogurt milk blend with improved heat stability suitable for making yogurt.
2. Description of the Prior Art
Yogurt is a combination of dairy ingredients such as whole milk, partially skimmed milk, skim milk, non-fat dry milk and the like which have been cultured to a specific acidity with an appropriate bacterial culture following heat treatment at elevated temperatures. Production begins with the homogenization and pasteurization of the dairy ingredients at high temperatures followed by cooling to 40.degree. C. to 50.degree. C. for inoculation with the culture. The culture is allowed to grow, produce acid, and reduce pH to a level where curdling or coagulation will occur.
Recently, calcium has received increased attention in dietary regimes because of its possible role in the prevention of diseases such as osteoporosis, hypertension and colon cancer. Calcium is a major mineral and essential in human nutrition. It is the most abundant cation in the body where approximately 99% of the calcium occurs in the bones and teeth providing an exchangeable pool of calcium, strength and structure. The remaining one percent is widely distributed in cells and body fluids and is responsible for the regulation of a number of metabolic functions such as nerve impulse conduction, muscle fiber contraction, hormone secretion, blood coagulation, normal heart beat, activation of enzymes and maintenance of cell membranes. The reference daily intake (RDI) for calcium is currently 1000 mg for adult males and females. Dairy products represent an excellent source of calcium, and in Western countries, the RDI for calcium is primarily met through the consumption of dairy products. It is generally believed that certain disease states, such as osteoporosis, are a result of habitual low intakes of calcium throughout the life span, related to low intakes of dairy products. Currently, it is recommended that individuals at risk for calcium-related disease, particularly Caucasian and Asian women in relation to osteoporosis, increase their calcium intake to a minimum of 1000 mg calcium per day.
Accordingly, a need exists for calcium fortified food products which will provide larger amounts of calcium in a single serving. A calcium-fortified yogurt would meet the needs of individuals at risk for calcium-related disease and provide individuals who choose not to consume large amounts of dairy products an alternative to tablet supplements to meet their calcium requirements.
Calcium enriched yogurts have been developed and used from time to time in the past. However, until development of the present process, calcium fortified yogurts have had serious drawbacks such as off-taste, insufficient heat stability, and cumbersome preparation steps which require the addition of sterile calcium to the yogurt after pasteurization.
The difficulties encountered when preparing a calcium fortified yogurt are primarily due to the heat sensitivity of the milk proteins upon the addition of ionic calcium. More specifically, the addition of ionic calcium to a milk system results in a pH decrease which is partially responsible for observed protein precipitation upon application of heat. Thus, many prior art yogurts circumvent the foregoing heat stability problems by adding sterile calcium sources after the heat treatment/pasteurization steps. This procedure is, however, cumbersome and uneconomical.
Many calcium fortified dairy products which have appeared in the retail market are fortified with tricalcium phosphate (TCP) and some hydrocolloid stabilizers. Since the solubility of TCP is very low, it does not seriously affect the heat stability of the product and can safely be added prior to pasteurization. Milk and yogurt fortified with TCP are, however, unacceptably gritty, sometimes with noticeable sedimentation of the TCP which can foul the manufacturing equipment.
In the article to Fligner, et al., Cultured Dairy Products Journal, pp.5, February 1988, a low-fat yogurt product fortified with calcium gluconate is disclosed. The article clearly states, however, that since the calcium gluconate-milk blend was not heat stable, calcium gluconate addition must take place after pasteurization.
U.S. Pat. No. 4,784,871 discloses a method for preparing a calcium fortified yogurt wherein an acid soluble calcium salt is added to fruit flavoring which is subsequently combined to the yogurt base. The calcium addition occurs after pasteurization of the yogurt base.
Accordingly, it is an object of the present invention to provide a process for preparing a calcium fortified yogurt with minimum change from normal yogurt processing. A further object is to prepare a calcium fortified yogurt with improved heat stability. Still another object of the invention is to prepare a calcium fortified yogurt that does not suffer from off-taste or undesirable sedimentation of the calcium source.